Is there a node in Lux with a similar function as Cycles' Fresnel and Layerweight nodes?
Short answer: No.

The problem is that such a texture is only possible in a unidirectional pathtracer, but LuxCore also supports bidirectional pathtracing. I have recently investigated this and implemented the basic math operation behind Cycles' layer weight node in LuxCore, but it leads to wrong results when using the lighttracing or bidirectional engines in LuxCore (you can read more and see pictures here).

It would not be hard to implement for the pathtracing engines, but it would make materials inconsistent when switching between engines. Imagine importing some assets for your scene, rendering with bidir and seeing a lot of artifacts. So I chose not to implement it - others might have different opinions.